High-speed low-power connectivity over a short communication link are prevalent in a variety of applications. Typically, a single integrated circuit (IC) (or “semiconductor”, “chip”) connects to another IC over a distance in the millimeter or centimeter ranges. High speeds cause the communication link (or “line”, “channel”) to act like transmission lines therefore termination is needed on both ends (both ICs). The terminations absorb the received signal to minimize or eliminate any signal reflected. However, termination at both ends results in increased power consumption.
A technique to reduce power is to use source-termination where the source was terminated, with typically a 50 Ohm resistance, and no far-end (or “destination”) termination. A major drawback of an unterminated receiver in wireline signaling is the slow absorption of signal reflections, which causes transmission bandwidth limitations, particularly with longer channels. The longer the channel, the longer the settling time of the (signal) reflections, and therefore, the lower the error-free signaling rate. For instance, if previous symbol(s)' reflections do not settle to a low enough amplitude before the next symbol in the line arrives at the receiver, the reflections can corrupt the next symbol unless they are cancelled.
At high speeds, all sort of capacitance parasitics are introduced into the signal being transmitted from one end to another or from one device to another. These types of parasitics are negligible with links or connections within an IC, but they are typically large enough external links between two ICs and thus result in considerable performance degradation of the signal traveling over such links for instance. For example, electro-static discharge (ESD) devices are used at IC pads, typically made of diodes, to absorb the electrical shocks but this leads to additional capacitance at the IC pads and at high speeds, the impedance associated with ESD capacitances cannot be neglected.
In high-speed wireline communication, over an impedance-controlled transmission line, typically, both sides of the wireline are terminated and the high-bandwidth signal is maximally absorbed at both ends of the wireline (or link). Accordingly, the reflection settling times are minimized. However, double termination comes at a cost such as increased power and decreased signal (or lower performance).
Accordingly, a circuit is needed for increased performance and reliability and lower power consumption for communications systems.